Crowd of a million people or more gathers to witness Pope Francis make saints
of two of his predecessors, in an event unprecedented in the 2,000-year
history of the Catholic Church

He shed blood in St Peter's Square during a failed assassination attempt and on Sunday a vial of John Paul II's blood formed the centre-piece of a ceremony in which the Polish pontiff was made a saint along with a predecessor, Pope John XXIII.

An ampoule filled with blood taken from John Paul II after he survived the 1981 assassination attempt by a lone Turkish gunman was reverently kissed by Pope Francis at the climax of an outdoor ceremony in St Peter's Square watched by an estimated 800,000 people in the Vatican and on giant screens in the surrounding streets of Rome. Millions more tuned in around the world.

Catholic pilgrims from dozens of nations, many of whom had camped out on the streets and in piazzas overnight, flooded into St Peter's Square at dawn to witness an event with no precedent in the history of the Catholic Church " the canonisation of two former popes by two of their living successors, Francis and Benedict XVI, the 87-year-old Pope Emeritus.

Wearing white papal vestments, Benedict looked frail 13 months after his historic resignation from the Seat of St Peter, was embraced by a smiling Pope Francis at the beginning of the service.

The Polish pope's blood, contained in an ornate reliquary decorated with silver olive branches, was presented to Pope Francis by Floribeth Mora, a Costa Rican woman whose sudden recovery from an inoperable brain aneurism in 2011 was declared the second miracle that was required for John Paul to be made a saint.

It was placed on a table near the high altar and stood alongside a relic from John XXIII - a piece of skin, encased in a similar reliquary, that was taken from his exhumed body when he was beatified in 2000, the first step towards being made a saint.

"Some people may be turned off by the concept of reliquaries, but it's a very beautiful part of our faith tradition," said Father Thomas Rosica, a Vatican spokesman.

"It's a sign that the saints are still with us, that they don't fade away." John Paul II declared more saints - 482 - " than all of his predecessors combined.

Benedict canonised far fewer, just 44, but the pace has picked up again under Pope Francis in just over a year. In May last year he canonised in one go more than 800 Italian martyrs from the 15th century who were massacred by the Ottomans for refusing to convert to Islam.

Asked why the Catholic Church continued to make saints, a process regarded by some as arcane, if not medieval, in the 21st century, Father Fr Rosica said: "Because they are heroes and the world needs heroes. They are role models for the rest of us as we try to live a holy life. But canonisation is not a proclamation of perfection."

While the jubilant crowds waved their national flags and cheered wildly when Pope Francis swept by in his white Mercedes Pope-mobile at the end of the service, there are Catholics question the whole concept of canonising popes, saying it is far too political.

"Modern popes bring with them a certain amount of political baggage. If you canonise a pope, it can be seen as a way of one faction protecting their favourite and enshrining his legacy," said John Thavis, a Vatican analyst and the author of The Vatican Diaries, a best-selling book about intrigue and dysfunction inside the Holy See.

Victims of sex abuse by paedophile priests were also staunchly opposed to John Paul's canonization, arguing that he turned a blind eye to reports of abusive clergy from dioceses around the world.

The result was "thousands" of children being raped and molested by predatory priests whom the Church chose to protect rather than bring to justice, victims' groups claim.

John Paul has also been sharply criticized for his support for Marcial Maciel, a Mexican priest who founded the Legionaries of Christ movement, who was revealed to have fathered several children and to have sexually abused them as well and other minors, as well as being a drug addict.

Pope Francis has been careful to show no trace of favouritism towards either John XXIII, a progressive who initiated key reforms to the Church under the Second Vatican Council of the 1960s, and John Paul II, a conservative who tried to roll back some of those changes.

"We declare and define as saints the blessed John XXIII and John Paul II," Francis said in a Latin prayer from the altar in front of St Peter's Basilica.

The former pontiffs were "two men of courage", he told the crowds. "They were priests, bishops and popes of the 20th century. They lived through the tragic events of that century, but they were not overwhelmed by them. For them, God was more powerful, faith was more powerful."

Many of the pilgrims who had travelled to Rome were from John Paul II's homeland, Poland.

"It's very exciting for us," said Lidia Pelic, 54. "To have four popes in one ceremony is a once-in-a-lifetime event. John Paul is our saint, just like St Patrick is for the Irish."

Among the dignitaries, royalty and heads of state from around 90 countries to attend the ceremony, the most controversial was Robert Mugabe, the president of Zimbabwe.

He is barred from entering the European Union because of alleged human rights abuses and vote- rigging at home, but the ban does not apply to the Vatican City State, which is not a member of the EU.

President Mugabe, a Catholic, also attended Pope Francis's inaugural Mass last year.